Almost every hydraulic applications use hydraulic pumps. A pump performs the task of converting mechanical energy into hydraulic energy. It intakes the fluid from the reservoir and transfers it to other components in the system through pipings. From the simplest hand pumps to complex piston and gear pumps, you can find many classifications of hydraulic pumps. The hand pump requires mechanical force to initiate the operation, whereas, the complex pumps use electric motors to activate hydraulic pumps. Forestry equipment, mining machinery, excavators, dump trucks, cranes, graders, loaders, etc.. use the applications of hydraulic pumps.
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Positive displacement and non-positive displacement are the two main classifications of hydraulic pumps. The non-positive hydraulic pumps produce continuous flow and the positive displacement pump produces an approximate constant flow at fixed speed irrespective of the pressure changes. Here, we will discuss a specific positive displacement pump called the variable displacement pump.
The variable displacement pump converts mechanical energy(rotation of motor or engine) to hydraulic energy. But, some variable piston pumps will perform opposite operations also. That is, conversion from hydraulic energy to mechanical energy(the function of the hydraulic motor). The flow rate and outlet pressure of the variable displacement pump can be changed during its operation. These pumps are commonly used to power a wide variety of tools. But, such pumps are more complex and expensive compared with others.
Construction, mining, agriculture, oil and gas industry and many other industries use the applications of variable displacement pump. These pumps don’t require manual control. The valves that control the speed of the actuators will control the fluid flow rate. So, variable displacement pumps are more energy efficient than fixed displacement pumps.
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In Variable displacement pumps, heat is not generated by moving oil around the circuit when no actuator work is being done. These pumps produce energy only when it is required. Also, these pumps reduce the use of flow control and pressure control valves.
Piston pumps and Vane pumps are the two categories of variable displacement pumps. The wide volumetric & pressure efficiency range of variable displacement piston pumps makes it popular than vane pumps. More details about these pumps are provided below.
Variable Displacement Piston Pump
High efficiency, ease of operation at high pressure and various applicable control types are the advantages of piston pumps. Pistons, the piston or cylinder block, valve plate, piston shoes, swash plate, and the drive shaft are the important components in a piston pump. Axial piston pumps, radial piston pumps and bent axis piston pumps are the common types of piston pumps.
The pumps that convert the rotary motion of an input shaft to axial reciprocative motion of the piston are called axial piston pumps. In bent axis piston pumps, the axis of the cylinder block is bent for producing reciprocative action of the piston. For radial piston pumps, the pistons are aligned radially on the cylinder block.
Variable Displacement Vane Pump
A vane pump contains a number of vanes slide in slots in a rotor and it can be converted to pressure compensated pump by replacing the hand wheel. Pressure compensated pumps mean, the pump operation ceases when the pump attains a certain pressure. For each revolution, variable displacement vane pumps deliver the same volume of fluid. Direct operated and pilot operated are the two types of variable displacement vane pumps.